What a lock actually does

A canal lock is simply a watertight chamber with a gate at each end. Close both gates and the water inside can be raised or lowered until it matches the level of the canal beyond the gate you want to pass through. There is usually room for two or three narrowboats, though some locks are far shorter.

The clever part is that your boat never climbs anything. The water does the climbing, and your job as crew is to control how quickly it moves and keep everyone safe while it does. Get that idea fixed in your head and the rest of lock operation starts to make sense.

The parts of a lock: gates, paddles and ground paddles

Every lock has a pair of gates at the top, the higher end, and another pair at the bottom. They look enormous, but they are beautifully balanced, so one person can usually push them open once the water either side is level.

Paddles, sometimes called sluices, are the valves that let water in or out. There are two main kinds:

• Gate paddles are fitted directly onto the gates. They let water through the gate itself, often with a fair bit of turbulence.
• Ground paddles sit in the lock wall, or ground, beside the top gates. Water arrives through a culvert beneath the lock and rises gently from the bottom, which is far calmer for a boat.

Most paddles are raised with a windlass, a T-shaped handle that fits the spindle on the paddle gear. Some locks have hydraulic or electric gear instead, and bottom gates usually carry smaller paddles that drain the chamber through culverts.

Filling the lock: heading uphill

If you are coming up from below, the chamber will normally be empty. Once your boat is inside, close the bottom gates and check that the paddles in them are fully down. Then, on the lockside, raise the ground paddles at the top end first, using the windlass.

Do this gradually, in stages. Water pours in through the culverts, the boat rises, and you pause to let the surface settle before winding a little further. Only use the gate paddles if the ground paddles alone are slow, and open them cautiously.

As the chamber fills, the incoming water pushes the boat gently forwards towards the top gates and the cill, the hidden step just below the water at the top end. Keep the boat well back from both, holding a centre line around a bollard or using a touch of engine. When the water inside is level with the canal above, the top gates will open easily. If they will not shift, the levels are not equal yet, so wait.

Emptying the lock: heading downhill

Going downhill is the reverse, and it feels quite different. Bring the boat in from the higher level, close the top gates and check their paddles are down. Then raise the paddles in the bottom gates, again a little at a time. Water drains away through the culverts and the boat sinks gently away from the top gates.

The risk here is a sudden surge. Crack the paddle open, wait, then raise it further. The boat should sit still. If it starts drifting backwards towards the bottom gates, close the paddle and let the flow settle before trying again. Once the water is level with the canal below, open the bottom gates and motor out.

Working safely and following instructions

A lock is heavy moving machinery, and water is deceptively powerful. A few habits keep everyone out of trouble:

• Follow the instructions of the lock keeper or an experienced crew member on board without question. Some locks, especially on river navigations and staircases, are keeper-operated for good reason.
• Never jump across the gates or stand on the paddle gear.
• Keep fingers, feet and loose clothing clear of ropes, windlasses and gate edges.
• Locksides are wet and slippery, so wear grippy shoes and take your time.
• Supervise children at all times and keep them away from the lock edge.

Staircase locks, where two or more chambers share gates, must be worked in a set order. Never drain a staircase from both ends at once, and if you are unsure, ask before you touch a paddle.

Practical tips and lock etiquette

• Leave the lock as you would like to find it: gates closed and every paddle wound down.
• If a lock is already set in your favour, with gates open and the chamber ready, do not change it unless you need to.
• Two crew can share the work neatly, one on the windlass and one on the boat. Agree your signals before you start.
• Watch for other boats approaching. Waiting for them saves water and earns you goodwill.
• Keep the engine in neutral while the lock fills or empties unless you need a touch of power to hold position.
• Take it slowly. There is no prize for speed, and a calm lock is a safe one.